1. Field of the Invention
The present invention relates to an optical device and a projection-type display apparatus and, in particular, to an optical device capable of irradiating an object with a light from a light source, while assuring a uniform illuminance distribution and a uniform color distribution on the surface of the object, and a projection-type display apparatus for irradiating a light modulation element with light from a light source and projecting the light modulated by the light modulation element onto a screen as an enlarged image.
2. Description of the Related Art
There are conventional projection-type liquid crystal display apparatuses using a transmission-type liquid crystal panel.
FIG. 19 in the attached drawings shows a conventional projection-type liquid crystal display apparatus.
The projection-type liquid crystal display apparatus 80 is a three-plate system apparatus in which a white light is separated into three primary color light beams. The beams are a red light beam (R light or R), a green light beam (G light or G) and a blue light beam (B light or B), and after modulating the three light beams, the three light beams are combined and the combined modulated light is projected. This projection-type liquid crystal display apparatus 80 comprises a light source 81 emitting a white light, a UV/IR cut filter 82 for removing the ultraviolet light component and the infrared light component of the white light, a GR reflection dichroic mirror 83 for reflecting the green light and the red light and allowing the blue light to pass through, R reflection dichroic mirrors 84A and 84B for reflecting the red light and allowing the green light and the blue light to pass through, total reflection mirrors 85A and 85B, a BR reflection dichroic mirror 86 for reflecting the blue light and the red light and allowing the green light to pass through, condenser lenses 87R, 87G and 87B, liquid crystal panels 88R, 88G and 88B for modulating respective color light beams, and a projection lens 89.
A halogen lamp or a metal halide lamp is used as the light source 81. The white light emitted from the light source 81 enters the UV/IR cut filter 82 where the ultraviolet light component and the infrared light component are removed, after which the blue light is transmitted through the GR reflection dichroic mirror 83, while the red light and the green light are reflected and the light path thereof changes by 90.degree.. The light path of the blue light is changed by 90.degree. by the total reflection mirror 85A, and after being condensed by the condenser lens 87B, enters the liquid crystal panel 88B. The blue light is modulated in accordance with image signals by the liquid crystal panel 88B, and the modulated blue light exits from the liquid crystal panel 88B. The modulated blue light is reflected by the BR reflection dichroic mirror 86 and, after the light path thereof is changed by 90.degree., proceeds toward the projection lens 89.
The red light in the green light and the red light reflected by the GR reflection dichroic mirror 83 is reflected by the R reflection dichroic mirror 84A and the light path thereof is changed by 90.degree. while the green light is transmitted through it. The reflected red light is condensed by the condenser lens 87R before entering the liquid crystal panel 88R. The red light is modulated by the liquid crystal panel 88R in accordance with image signals, and the modulated red light exits from the liquid crystal panel 88R. The modulated red light is reflected by the R reflection dichroic mirror 84B and the light path thereof is changed by 90.degree., while at the same time being combined with the blue light. The resulting light is reflected by the BR reflection dichroic mirror 86 and, after the light path thereof is changed by 90.degree., proceeds toward the projection lens 89.
The green light transmitting through the R reflection dichroic mirror 84R is condensed by the condenser lens 87G before entering the liquid crystal panel 88G. The green light is modulated by the liquid crystal panel 88G in accordance with image signals, and the modulated green light exits from the liquid crystal panel 88G. The modulated green light, after changing its light path by 90.degree. at the total reflection mirror 85B, is transmitted through the BR reflection dichroic mirror 86 to be combined with the blue light and the red light, and proceeds to the projection lens 89.
The combined light that has entered the projection lens 89 is projected to a screen, not shown, thereby forming an image on the screen.
By the way, the condenser lenses 87R, 87G and 87B arranged adjacent to the liquid crystal panels 88R, 88G and 88B, respectively, assure that the modulated light that has left each liquid crystal panel enters the projection lens 89 efficiently.
FIG. 20 shows a light source used for the projection-type liquid crystal display apparatus described above.
As shown in FIG. 20, the light source 81 is configured of a light-emitting unit (arc) 92 and a reflector 91 for reflecting the light from the light-emitting unit 92 in a predetermined direction.
Also, in the case where the light source 81 is a discharge lamp of a DC energization type, an anode 93 and a cathode 94 are arranged in opposed relationship to each other on the optical axis in the light-emitting unit 92.
When the light source 81 of this configuration is used, the illuminance distribution on the surface of each of the liquid crystal panels 88 (R, G, B) which is irradiated with the light from the light source 81 is such that the illuminance is highest at the central portion of the surface and progressively decreases toward the peripheral portion.
Also, in the projection optical system of the conventional projection-type liquid crystal display apparatus 80, the transmittance characteristic of the projection lens 89 is such that the transmittance is highest in the neighborhood of the optical axis of the lens and tends to progressively decrease toward the peripheral portion.
As a result of these two factors being combined, the image projected on the screen is bright at the central portion of the screen but becomes darker toward the peripheral portion, thereby leading to the problem that the illuminance distribution becomes uneven.
Also, in the case where the light source 81 is a lamp of a DC energization type or the like which has a color distribution in the light-emitting unit 92, the color is distributed on each of the surfaces of the liquid crystal panels 88 (R, G, B) which is irradiated with the light from the light source 81, resulting in the problem that the color distribution of the image projected on the screen becomes uneven at the central portion and the peripheral portion of the screen.
Specifically, if it is assumed, for example, that the side of the anode 93 includes a blue component and the side of the cathode 94 includes a yellow component in the light-emitting unit 92 of the light source 81, in the light paths of the light rays reflected at the same point of the reflector 91, the light ray Lc exiting from the cathode side indicated by dashed line is reflected toward the optical axis and illuminates the optical axis side, i.e. the central portion of the radiation surface. The light La exiting from the anode side indicated by the solid line, on the other hand, is reflected in the direction away from the optical axis and illuminates the peripheral portion of the radiation surface.
Consequently, the image projected on the screen becomes yellowish at the central portion of the screen near the optical axis, and bluish at the peripheral portion. As described above, in the conventional projection-type display apparatus, the problem is that the illuminance distribution and the color distribution of the image projected on the screen become uneven.